Electrical systems with packaged electrical and electronic components are known and are in use. For example, Motor Control Centers (MCC's) are used for power and data distribution in large and industrial operations. In MCC's, a variety of components, such as switchgear, semiconductor power electronic circuits, programmable logic controllers, motor controllers, and so forth, are housed in large electrical enclosures that may be subdivided into sections or columns, which may be further subdivided into compartments. The MCC includes associated bus bars, interconnections and supporting structures for distribution of electrical power to the various compartments.
Typically, the MCC is connected to a main power line that may feed three-phase AC power to horizontal bus bars of the MCC. The horizontal bus bars, in turn, may feed the three-phase power to vertical bus bars disposed in each of the sections or columns of the MCC. The vertical bus bars, in turn, may feed the three-phase power to various units (which typically include electrical components) that are installed in compartments of a section. The units, in turn, may provide power terminals (conductors), such as copper bus bars, for feeding the three-phase power to a system environment, such as motors, as may be required for various applications.
Units are typically plug-in or “withdrawable” in that they often use a set of stabs or contacts to connect to or disconnect from the MCC for mechanical and electrical engagement/disengagement. Such withdrawable units may be readily supplied by vertical distribution bus bars, and are convenient in that they may be more easily moved around or replaced than non-withdrawable units which are often screwed or wired to horizontal main bus bars of the MCC (also referred to as “fixed feed” or “frame mounted” units).
However, in some industries, such as mining, conductive or abrasive dust in the environment may make withdrawable units undesirable due to fretting corrosion and/or debris. Such hazards may cause contact intermittency and/or increased contact resistance for withdrawable stab contacts, which could thereby lead to a system failure.